A valiant Alessio Martinelli (Italy) soloed to silver 56 seconds behind Simmons. American Magnus Sheffield out sprinted the remains of the day's decisive break to join his fellow team mate on the podium.
Simmons' victory is the first America junior men's road worlds title in 28 years, but it was all part of a plan executed almost to the letter.
"We never knew exactly when we were going to go," the 18-year-old said. "But we knew (we were) going to try and get me and Magnus on the circuits and then I launched from there so it worked out maybe a little earlier than planned but it seemed to work!
"I had my eyes on this since November. I had a good feeling about this course. We had a really strong team. First of all I want to say a big thanks to all the guys they were on the front basically from km zero and Magnus set it up perfectly and I just found out he sprinted for third so a perfect day for America."
Simmons won a string of junior races in 2019 including Gent-Wevelgem. Within hours of pulling on the rainbow jersey, Trek-Segafredo announced the signing of he and junior men's ITT winner Antoni Tiberi.
"This is my last junior race obviously I'm really excited to be stepping up next year and seeing whether we can keep going."
The late break came just before the race hit the first lap of the finishing circuits, some 40kms from the line. But it was on from the gun in Richmond with the US, Great Britain and Italian teams all working hard to put the peloton into the hurt box. Multiple attacks were launched until Great Britain had Max Walker up the road with 81kms to go, the US working hard to rein him in 15kms later.